In recent years, digital cameras have been rapidly becoming smaller and the image size decreasing from 1/3 inch to 1/4 inch, thus increasing the demand for smaller lenses. Moreover, reduction of the number of lens elements and simplification of lens structure is being achieved in order to make the lenses smaller and to reduce the cost. However, there is a limitation in making an individual lens element of a lens group smaller due to restrictions imposed by production considerations. Hence it becomes important to arrange lenses having shapes that meet a production specification while satisfying a lens size requirement and maintaining good lens performance.
In a two-group zoom lens with a short overall length, the number of lens elements is naturally limited. Moreover, decreasing the number of lens elements results in a reduction in the number of parameters which are available for correction of aberrations, thus making it more difficult to attain a required optical performance. Furthermore, in the case of a lens in a smaller overall system, the space between a stop and a CCD image surface inherently becomes smaller, making it more difficult to move the position of the exit pupil away from the image surface by a certain distance. This causes the incident angle of light rays entering the image surface to become large and produces shading. In short, it has been difficult to satisfy the two opposing requirements of maintaining good optical performance and decreasing the size of the lens. Moreover, in digital cameras in particular, the quality of the still image is an important consideration; hence, distortion at the boundary of the image must be small.